The manufacture of semiconductor devices includes a variety of intermediate steps which involve the handling of individual wafers, die, substrates, and the like. Typically, such steps include breaking, sorting, inspection, storage, shipment and related wafer and die handling prior to die and lead bonding, and subsequent die encapsulation. A number of prior art die handling method and means currently are employed, which include the use of non-adhesive carriers, adhesive carriers, and compliant elastomeric retention carriers.
With non-adhesive carriers, die are handled on flat substrates, such as glass plates, or in sized cavities of multiwell trays. Such carriers have a low coefficient of friction with the die. As a result, with a flat glass carrier, the die are easily accidently disoriented on the carrier, or spilled off therefrom. Transportation, or shipment, on such surfaces is difficult. Cavity trays are useful to prevent sliding across the carrier surface. However, the cavities must be properly sized to roughly conform to the die size. Also, die may rotate within the cavity such that precise die orientation is not retained. Further, die edge damage may occur within the cavity during shipment, and die removal from the cavity is sometimes inhibited because of the proximity of the die edge to the cavity wall.
Conventional adhesives are sometimes used to temporarily retain the wafer, or die, on the carrier to facilitate handling thereof. Such adhesives may involve waxes which are inconvenient to handle, and/or adhesives which may leave a residue on the die or wafer which interferes with subsequent processing, such as die bonding. Often, special equipment is required to remove the die from the adhesive substrate. Further, adhesive qualities are not always uniform and are difficult to control, particularly at the low tack levels ordinarily required.
Compliant or elastomeric retention carriers include the use of rigid or semirigid substrate having a resilient, rubber-like, layer, such as an elastomer, thereon for support of the die. Wafers and die are tightly held in position on the carrier by frictional and interfacial forces, rather than by adhesive forces. These carriers have several advantages in that they leave no adhesive residues, they are flat and therefor do not inhibit access to the die as by a vacuum collet or tweezer, and they do nor require an array of die-sized cavities for support of different sized die. However, while die retention using such an elastomeric surface is favorable, die removal presents substantial difficulties. The intimate contact between the smooth die surface and smooth elastomer surface causes the die to "stick" to the carrier. Frictional engagement is desirably high if one attempts to slide the die off from the carrier, but a partial vacuum tends to be created between the die and carrier if an attempt is made to lift the article from the carrier. Consequently, the die cannot readily be removed using conventional tweezers or vacuum techniques.